Performance of Li4Ti5O12-based reference electrode for the electrochemical analysis of all-solid-state lithium-ion batteries

The establishment of three-electrode cells for all-solid-state lithium-ion batteries is an important issue to clarify the electrochemical behavior of the battery components and solve problems for the practical applications. Here we prepared an all-solid-state three-electrode cell with a chemically-reduced Li4Ti5O12 reference electrode and investigated electrochemical properties of a LiCoO2 composite electrode in a Li-In|Li10GeP2S12|LiCoO2 cell. Plateau potentials in charge-discharge curves were coincident with reported values. Cell impedance measured with two-electrode configuration agreed well with the sum of the impedances of the positive and the negative electrodes measured with the reference electrode. These results show that chemically-reduced Li4Ti5O12 reference electrode was worked as a Li7Ti5O12|Li4Ti5O12 reference electrode and electrochemical properties of the LiCoO2 electrode and the Li-In electrode were separated. From the temperature and the state of charge dependences of LiCoO2 impedance, resistances related to interface or interphase and charge-transfer reaction were identified. These results show that all-solid-state cells with chemically-reduced Li4Ti5O12 reference electrodes are promising candidates for three-electrode cells for all-solid-state lithium-ion battery systems.